1. Field of the Invention
The present invention relates generally to mobile grain harvesting equipment such as the combine harvester in which means for measuring the absolute grain loss as a function of the input grain flow on the area harvested is desired.
2. Description of the Prior Art
As mobile combines are harvesting in the field, the grain is threshed and separated from the straw and stored in a storage bin within the combine for later delivery to another vehicle for transport from the field. The material harvested enters the combine through a header portion and is elevated through the elevator housing into the threshing and separating units within the combine. The threshing separating units receive unthreshed crop material and generally separate the grain from the straw by means of a rubbing or beating motion. The grain and other unthreshed crop material separated from the straw falls from the threshing and separating units onto the grain handling and cleaning means, while the straw is discharged from the rear of the separating unit through an opening in the hood of the combine. The grain handling and cleaning mechanism includes means to separate the light straw or chaff from the grain and means to segregate the unthreshed material (known in the art as tailings) from the grain in order to collect the clean grain in a grain bin or tank located at the top of the combine. The grain handling and cleaning mechanism comprises an oscillating grain pan, oscillating sieves and a fan. The grain pan, disposed beneath the threshing and separating units, receives the threshed material therefrom and discharges the threshed material to oscillating sieves disposed rearwardly and below the grain pans. The vibration or oscillation of the grain pan causes the threshed material to move rearwardly to be discharged onto the sieves below and thus subjected to the air flow from the cleaning fan. The fan, moreover, blows a sufficient volume of air through the apertures provided in the sieves to aerodynamically separate the grain from the chaff. Accordingly, the chaff and other small trash material are suspended in the airstream and are discharged through a rear opening in the combine while the grain drops to the sieves below. The upper sieve or chaffer is provided with means for adjusting the apertures such that the grain received thereon may fall therethrough while the larger trash material is shaken rearwardly for discharge from the combine. In addition, the lower or cleaning sieve disposed beneath the chaffer sieve includes adjustable apertures such that only the grain drops therethrough to a guide where it may be collected for elevation to the grain bin. Any larger material (generally known in the art as tailings) which falls onto the lower sieve is discharged rearwardly and collected within the combine to be elevated and returned into the feed section of the threshing and separating units for reprocessing of the grain attached thereto. If the combine harvester is improperly adjusted or operating at an inefficient ground speed, a substantial quantity of grain will not drop through the chaffer sieve for cleaning on the cleaning sieve. This grain, along with the chaff and other small trash material, is discharged through the rear opening in the combine while most of the grain drops to the cleaning sieve below. This source of grain loss is particularly significant in a combine harvester having axial flow threshing separating units such as the one disclosed in U.S. Pat. No. 3,669,122 and assigned to the Applicant's assignee. The axial flow type combine harvester differs from the more conventional combine harvester in the design of the threshing and separating means, and as a result the axial flow type combine harvester has negligible grain losses from the separating means under most harvesting conditions. Whereas, in the more conventional combine harvester the straw walker separation means is the predominant source of losses. Thus, there is an especially important need for determining the absolute grain loss which results from grain being discharged beyond the rearward portion of the chaffer sieve in an axial flow type combine harvester.
The methods for measuring grain loss fall into two general categories which are independent of the sensing technology utilized. These categories may be referred to as direct measurements and indirect measurements. The indirect measurement category would include methods which measure the internal grain flow to calculate the amount of grain discharged from the combine. Whereas, a direct measurement is one in which the material discharged through a rear opening in the combine contains dust, straw, chaff, and grain, and the amount of grain contained therein is monitored by a sensor which responds to the grain in a fashion which is distinctive from the responses produced by the other materials. The ability to discriminate between grain and the other materials is crucial to a successful direct measurement. Since the kernel of grain is much harder than the straw and chaff, acoustic impacts on sensors have been utilized to detect the presence of grain in the trash materials. The impact of grain on a resilient surface coupled to a piezoelectric transducer induces output signals having a relatively fast rise time and a damped sinusoidal decay which is characteristic of this type of sensor. These acoustic sensors, however, may not accurately detect the presence of grain impactions when harvesting conditions vary or when the grain flow rate is too great to be resolved into individual impactions. Acoustic sensors of this type have heretofore been disclosed in several prior art patents for use in grain loss monitors. For example, a grain loss monitor for a combine harvester utilizing an acoustic sensor and responsive to a single varying harvesting condition, i.e. ground speed, is disclosed in U.S. Pat. No. 3,935,866, issued Feb. 3, 1976, assigned to Allis-Chalmers Corporation and entitled "Grain Loss Monitor". The disclosed grain loss monitor derives a grain loss rate signal in accordance with the number of grain impactions upon an impact sensor and a ground speed signal proportional to the ground speed of the combine. The grain loss rate signal is divided by the ground speed signal to drive an analog display of the grain loss per unit area which is independent of time. The preferred embodiment of this invention includes a one shot multivibrator which is triggered to its unstable state to generate a fixed width pulse each time a kernel impacts the acoustic sensor, a tachometer coupled to the combine wheels and a period time integrator triggered by the tachometer pulses derive a unidirectional ground speed voltage inversely proportional to the frequency of the tachometer pulses. A pulse frequency modulation chopper circuit is turned on and off by the fixed width one shot pulses and has its peak voltage controlled by the unidirectional ground speed signal for accomplishing division of grain loss rate by the combine ground speed. An averaging circuit determines the average voltage of the chopper output pulses as an analog of the grain loss per unit area, thus providing the grain loss indication. This grain loss indication, however, is subject to inaccuracies, since harvesting conditions other than ground speed vary the total amount of grain discharged through the rearward portion of the combine harvester. Additionally, the acoustic impact sensor samples only a portion of the discharged material, which varies as a function of the ground speed, pitch angle, roll angle, and crop conditions. Furthermore, there is a significant problem of grain adhesion in moist crops which drastically reduces the proportion of loss grain which is free to impact upon the acoustic sensor. Thus, the accuracy of this grain loss monitor is severely constrained by harvesting conditions.
Another grain loss monitor utilizing acoustic sensors is disclosed in U.S. Pat. No. 4,036,065, issued on July 19, 1977 to Strelioff et al, and assigned to Senstek Ltd. Acoustic sensors are disposed across the rear of a sieve of a combine to sense a percentage of the grain lost, and the sound is picked up by a microphone, amplified, filtered and fed to a ratio computing device which calculates the total grain loss from the sampling and displays it on a meter. A second sensor samples grain passing through the rear portion of a straw walker, and since the sample is representative of grain passing over the end of the straw walker, it can be used to calculate the grain loss over the end of the straw walker. The sound from the second sensor is picked up by a microphone, amplified, filtered and fed into a ratio computing device and displayed on a meter. The two grain losses may be displayed individually or collectively. In any event, the Senstek apparatus, like the Allis Chalmers apparatus, is subject to the inaccuracies induced by varying harvesting conditions.
Accordingly, there is a need to provide the agricultural machine industry with a solution to the problem of determining the absolute grain loss of a combine harvester under the widely varying conditions which are present during typical harvesting operations. The acoustic impact sensors which are positioned to sample only a percentage of the grain provide the only direct measure of absolute grain loss, but these measurements are very qualitative in nature and subject to wide variations and therefore to interpretation. The practice of the present invention which would provide for an indirect measurement of absolute grain loss, therefore, would provide the agricultural machine industry with a solution to the problems associated with the measurement of absolute grain loss.